Spark plug



Oct. 19, 1937. A. A. KASARJIAN SPARK PLUG Original Filed Sept. 8, 1935 /0 KNO; I NaA/O, or Mercury,

Patented Oct. 19, 1937 UNITED STATES PATENT OFFICE Application September 8, 1933, Serial No. 688,550

Renewed March 17, 1937 11 Claims.

This invention relates to spark plugs and is directed more particularly to a spark plug so constituted as to withstand high compressions and high temperatures without overheating or causing preignition, this being accomplished according to the fundamental principle of this invention, by the provision of novel means for transferring away the heat from firing end of the plug, and distributing it to and dissipating it at the cooler parts of the plug.

In spark plugs and especially those used in aircraft engines, it is imperative that the firing end of the central electrode of the plug, which is directly exposed to the heat of the combustion charge be made of material which will withstand high temperatures without scaling or erosion. It is well recognized, however, that metals which have the capacity of withstanding such heat are relatively poor heat conductors, so that in ignition plugs for aviation which embody a central electrode of heat resisting material, it is common for such electrode to become heated gradually to such extent as to become incandescent and cause preignition of the fuel. Obviously, preignition will develop even greater heat, resulting in general over heating of the engine which cannot be tolerated.

It has been heretofore suggested as a possible solution for this diiiiculty to make the central electrode of the plug of ample, that portion of the plug which is adopted for direct contact with the heat of the explosive charge which is known in the art as the spindlehead, is made of heat resisting material while the spindle shank which forms the remainder of the electrode is made from a material susceptible of greater heat conductivity, the head and the shank being generally welded together. This arrangement is less apt to produce an incandescent condition of the spindle head in operation but does not solve the problem satisfactorily as the spindle head may even with this arrangement become heated in an extremely high compression aircraft engine and become overheated to such an extent as to cause preignition to which I have referred.

My experience with spark plugs has convinced me that it is absolutely essential for the proper functioning of the plug under all conditions that the excessive heat absorbed by the spindle head be carried away and dissipated rapidly and I have reached the conclusion as a result of a long experience and exhaustive experimentation that this cannot be satisfactorily accomplished solely by combination of two materials; that is, by

two materials, for ex-z making the spindle head of a heat resisting material and the shank of a metal possessing high coeflicient of heat conductivity. On the contrary, I have found that excellent results may be obtained by employing a spindle head of a high heat resistivity associating with it a spindle of high heat conductivity. This may be brought about by making the spindle hollow and filling it with a material possessing high heat conductivity; a material which will be liquefied under prevailing temperature, absorb heat by fusion and transfer heat from the spindle head to the cooler parts of the plug by convection as well as by conduction.

I find that some nitrate salts possess all of the 15 aforementioned characteristics. Excellent results were obtained by potassium nitrate, sodium nitrate or mixture of both. I do not mean to limit myself to these salts only- -other material, such as mercury may also be advantageously used. The underlying principle of the invention is to utilize heat of fusion, heat of vaporization and the heat conductivity of the material to absorb heat and carry it to cooler parts of the plug, by convection as well as by conductance, and dlssipate it there.

The core of the spindle is not filled completely.

A space is left to compensate for thermal expansion of the material used.

The spindle, in another form of the spark plug, may be left open by omitting the plug in the end thereof for the free flow of air into and out of the well formed therein.

A spark plug constructed by this principle is admirably suited for radial engines. Radial engines have a tendency of fouling the spark plugs in lower cylinders and overheating those in the upper cylinders. Spark plugs made with this method will run slightly hotter on the lower cylinder and cooler on the upper cylinder as the cooling medium will by gravity be in closer contact with the spindle head in the upper cylinders and somewhat away from it on the lower cylinders. Similarly, in the case of the open spindle, the heated air in the cores of the spindles of the spark plugs on the upper cylinders, being free to rise will establish a convection current of air with the outside cooler air going down the center of the core and replacing the rising heated air around it; while on the lower cylinders the heated air will tend to remain in the wells. This will be an ideal condition and will eliminate the necessity of using hot running plugs on the lower cylinders and C0018r plugs on the upper cylinders. This method, the use of two kinds of plugs in the same engine, is often resorted to now in aircraft enconjunction with the accompanying drawing.

The accompanying drawing illustrates the practical embodiment of the invention, but the constructions therein shown are to be understood as illustrative only and not defining the limits of the invention.

Fig. 1 is a cross section of a plug embodying the invention in its preferred form.

Fig. 2 is a like section of a central electrode structure embodying a modified form of the 1nvention.

. The plug structure of this invention maybe included in any conventional plug construction so far as the porcelain, mica, or base structure 1s concerned. However, for the purpose of illustration, I have shown the same in Fig. 1 of the drawing as incorporated in a well known plug of the aviation type.

In this figure, l designates the shell of the plug provided with grounded baffle type electrode 2. 3 is the bushing which holds the central electrode in place and this central electrode is designated generally by the reference character 4. The

1 method of holding the central electrode within the shell in the structure shown in Figure 1 is substantially that illustrated in the Mosler Patent No. 1,588,489 dated June 15, 1926, and in wh1ch patent the central electrode is secured in place by cooperating annular wedges 1, 8 and 9, which firmly support and mount the center electrode and its associated part upon the bushing 3 which is thereupon screwed into the shell I.

Carrying out the present invention with a plug of this character, as well as any other conventional plug structure, the center electrode is made hollow as shown by drilling or by some other suitable means. This hollow space may also be serrated to increase the internal surface when more rapid transfer of heat is required. The space is filled with a cooling medium l0, leaving a small void to compensate for thermal expansion of the said medium. The hole is then sealed by a plug H at normal temperature or after heating the spindle to the highest temperature that it would attain in operation, so as to produce a partial vacuum in the well when the plug is cold, thus helping to produce easier fusion and lowering the boiling point of the cooling medium, as well as facilitating turbulence. 7

The filling and sealing of the well of the center electrode is accomplished either before or after the assembly of the plug. The plug II is force fitted into its place and sealed by either soldering or welding.

In practice, the center electrode is made of one piece as shown in Figure 1, or of two pieces, the shank 5, and the head 6, as shown in Figure 2 and welded together as shown at I2. The head is of fusion and heat of vaporization of the said medium and partially is transmitted in an upward direction to the shank 5 and to the plug H and thereby to the cooler regions of the plug.

The plug of the present invention in any of the ways which I have described has proven to operate with marked efliciency as compared with prior practice. It possesses an unusual range of operation between fouling tendency of the low. compression and oily engines; and the preignition tendency of the high compression or hot running engines. By the use of this plug, the necessity of using cooler plugs in the upper cylinders and hotter plugs in the lower cylinders of aircooled engines is eliminated. This plug also eliminates the necessity of two or more kinds of plugs with varying heat ranges to take care of the requirements of low compression and high compression engines. This plug can be used universally in all the aircraft engines, as the spindle head temperature is not allowed to rise higher than the temperature at which the fuel may be ignited, neither is it allowed to fall below the evaporation temperature of oil which is the chief cause of fouling of the plugs.

In the accompanying drawing, I have illustrated the preferred forms of the present invention but the invention is to be understood as fully c'ommensurate with the appended claims.

Having thus fully described the invention, what I claim as new and desire to secure by Letters Patent is: a 1. In a spark plug, a central electrode hollowed throughout but closed at the inner end by a hollowed out head joined thereto by fusion, and at the outer end by a plug hermetically sealing the hollow space in the electrode, a cooling medium of relatively high heat conductivity partially filling the hollow electrode, said medium normally being a solid materialpossessing ability in service to absorb heat by a change of state, such as fusion, and thereupon to carry heat from the hotter to the cooler parts of the plug by convection as well as conduction.

2. In a spark plug, a central electrode of heat conductive material hollow throughout but closed at the inner end by a hollowed out head of a heat resistive material joined thereto by fusion, and at the outer end by a plug hermetically sealing the hollow space in the electrode, a cooling medium of relatively high heat conductivity partially filling the hollow electrode, said medium possessing ability in service to absorb heat by a change of state, and to carry heat from the hotter to the cooler parts of the plug by convection as well as conduction.

3. In a spark plug, a central electrode of good heat conductive material hollow throughout but closed at the inner end by a hollowed out head of a heat resistive material joined thereto by fusion, and at the outer end by a plug hermetically sealing the hollow space in the electrode, a cooling medium of relatively high heat conductivity partially filling the hollow electrode, said medium normally being a solid and possessing ability in service to absorb heat by fusion and vaporization and to carry the heat from the hotter to the cooler parts of the plug by convection as well as conduction.

4. In a spark plug, a central electrode of good heat conductive material hollow throughout but closed at the inner end by a hollowed out head of a heat resistive material joined thereto by fusion, and at the outer end by a plug hermetically sealing the hollow space in the electrode, a cooling medium of relatively high heat conductivity partially filling the hollow electrode,

a cooling medium of relatively high heat conductivity partially filling the hollow electrode, a said medium normally being a liquid and possessing ability in service to absorb heat by vaporization and to carry the heat from the hotter to the cooler parts of the plug by convection as well as conduction.

6. A central electrode such as claimed in claim 2 in which the cooling medium has been placed in the hollow electrode and hermetically sealed therein by the plug under substantially service temperatures so as to form avoid in the hollow at lower temperatures and thereby prevent excessive pressures under working conditions as well as make-it easier to obtain the change of state within the desired working temperature range.

7. A central electrode such as claimed in claim 2 in which the cooling medium is potassium nitrate and has been placed in the hollow of the electrode and'hermetically sealed therein by the plug under substantially service temperature so as to form a void in the hollow at lower temperatures and thereby prevent excessive pressures under working conditions as well as make it easier to obtain the change of state within the desired working temperature range. I

8. A central electrode such as claimed in claim 2 in which the cooling medium is sodium nitrate and has been placed in the hollow of the electrode and, hermetically sealed therein-by the plug under substantially service temperatures so as to form a void in the hollow at lower temperatures and thereby prevent excessive pressures under working conditions-as well as make it easier to obtain thefichange oi state within the desired working temperature range.

9. A central electrode such as claimed in claim 2 in which the cooling medium is a mixture of potassium nitrate and sodium nitrate and has been placed in the hollow of the electrode and hermetically sealed therein by the plug under substantially service temperatures so as to form a void in the hollow at lower temperatures and thereby prevent excessive pressures under working conditions as well as make it easier to obtain the change of state within the desired working temperature range,

10. In a spark plug, an insulator sleeve fitted with a central electrode of heat conductive material hollow throughout but closed at the inner end by a hollowed out head of a heat resistive material joined thereto by fusion at a point above v the bottom of the insulator sleeve.

11. A central electrode for a spark plug comprising a tubular portion of a good heat conductive material, set within an insulator sleeve, an electrode head joined to the end thereof by fusion andinclu'ding a shoulder which fits over the end of the insulator sleeve and a hollow there,- in open to the hollow of the tubular portion and extending beyond the plane of the shoulder, a

cooling medium hermetically. sealed within the I ARMEN A. KASARJIAN. 

